Emissive incandescent cathode



W. ESPE EMISSIVE INCANDESCENT CATHbDE Filed May 1, 1935 June 21-, 193.8.

WITNESSES:

INVENTOR I Patented June 21, 1938 UNITED, STATES 2,121,589 EMISSIVE INCANDESCEN'I CATHODE Werner Espe, Berlin-Siemensstadt, Germany,

' assignor to Westinghouse Electric & Manufeaturing Company, East Pittsburgh, Pa., a corporationof Pennsylvania Application May 1, 1935, Serial No. 19,233

In Germany June 28, 1934 2 Claims. (01. arm-27.5

- My invention. relates to cathodes and it has particular relation to cathodes having a vaporizable electron emitting substance.

' It is an object of my invention to provide a 5 cathode having a very long life. More specifically stated it is an object of my invention to provide a cathode in which a reservoir of electron emittingmaterial is contained within a porous metallic mass, whose pores are also permeated with the electron emitting material.

Other objects of my invention will become evident from the following detailed description, taken in conjunction with the accompanying drawing, in which:

Figure 1 is a. view, partly in elevation and partly in section, of a tube incorporating my invention,

Fig. 2 is a modification of the cathode structure illustrated in Fig. 1, and Fig. 3 is a still further modification of the cathode structure of Fig. 1.

Incandescent cathodes manufactured up to the present time have the disadvantage that their life is comparatively short, since the emissive material quickly loses its emissive power. The cathodes have been coated rather heavily to increase the life of this type of cathode. It has been found, however, that this thick outer surface has a comparatively large internal resistance, and local overheating results with the possibility of eruptions from the surface.

According to my invention, I extend the life of a cathode by utilizing a porous metallic mass permeated with electron emissive material, and I preferably'provide a pocket within this mass having an additional reservoir of electron emitting material.

In Fig. l is disclosed the container it having an anode ii and preferably a grid 92 therein of well-known construction. The cathode structure l3 preferably comprises a mass it. This mass is preferably a sintered porous body composed of numerous fine angular metallic particles, and is preferably permeated with vapor of an emissive material or has its pores filled with an emissive material vaporizable by heat. This cathode body is comparatively thick and may be, as shown, a cylindrical block, the heighth'of which may be substantially equivalent to its cross-section. While other materials may be used, I prefer to construct the body It of tungsten.

One method of constructing this body may be as follows. Barium azlde (Ba(Na) 2) and tungsten in pulverized condition are mixed and 86 formed into a body under high pressure. The

body thus contains barium throughout, and when the body is heated, the nitrogen evaporates in such a manner that a mixture of barium and tungsten remains. The barium serves as emissive material and permeates the whole body.

Tlmgsten-powder may also be heated to an incandescent temperature. approximately 700 to 800 and then sintered. Oxides are formed on its surface. The powder may then be compressed under high pressure temperatures that are lower than the decomposition temperature of the oxide and the body formed. Channels can be provided in the outer portion of the body,

, and these channels or pores permeated with an emissive material penetrating deep into the inner portion. As the emission takes place from the outer surface, the material distributed throughout the inner part of the body replenishes the vaporized portion from the surface.

These bodies, while being formed, could be dipped into an electron emitting substance, such as barium or barium compound. Many materials which are now well known are capable of use in these cathodes, but the material selected should be one that can be capablyabsorbed by the body. The body may be constructed of other sintered materials other than tungsten, and it is also conceivable that the sintering of the cathode body may be omitted. The body which is to absorb the emissive material should, however, be filled with numerous small spaces. The oxidizing of the surface of these pores aids in absorbing and holding the emissive material.

I also prefer to provide a pocket or recess it in the cathode body, and to provide. a reservoir it of vaporizable electron emissive material therein. This material may be an alkaline earth,

as for example barium, or an alkali, such as potassium or sodium. The barium vapor, if barium is used. diffuses through the whole body and produces on the walls of the recess and in the recess a precipitation which serves as the emissive material. If sintered tungsten powder is used as the cathode body materiahthen if the surface of the tungsten particles are slightly oxidized to have a tungsten oxide of a low order formed on the outer surface, a better adherence of the emissive material thereto is attained. If tungsten particles having a, basic oxide on their surface are utilized, then these tungsten particles can be formed by subjecting them to pressure at high temperatures below 900 C.

It is also possible to provide a cathode body by mixing aluminum with barium oxide and heating body, such as the filament II. The plate I! may take the form oi. a part of the casing wall and be sealed to the tube as at II. A connection 20 is made from one of the heating leads 2| to the metal plate I1, and in this way the plate ll forms a cathode connection to the cathode body l4. A separate lead-in connection may be made to the cathode, if desired. Any suitable support and closure member for the filament ll, such as the insulating plate 22, may be provided.

The material of the metal plate I! may be of copper or of other vacuum-tight metals. In case a separate lead-in to the cathode is desired, then the portion I! may be of insulating material or may be replaced by a cathode lead supported from the usual press.

Fig. 2 discloses a modification oi the cathode structure, in which the cathode body H has a recess l5 formed therein with a reservoir of electron emitting material I6. This recess I5 is preferably threaded, and a closure body 24, composed of sintered material, is threaded into the threads 25. This closure member 24 is used as a support and as a connecting element. The closure body 24 may have, if desired, a heating element or filament 26 disposed therein or only a single cathode connection thereto.

Fig. 3 discloses a still further modification in which channels ll are formed in the outer surface or portion of the body and a heating element 3| placed in these channels. The pores of the body l4 will act as wicks of electron emitting material heated at their outer ends.

From the foregoing description, it is apparent that the porous body l4 may have electron emitting material or vapor permeated throughout its construction. As the device is operated, this electron emitting material is gradually drawn out through the porous structure or this body. The electron emitting material II and the recess replenishes the part used up and provides a very much longer life for these indirectly heated cathodes over the structure of the prior art.

Although I have shown and described certain specific embodiments of my invention, I am iully aware that many modifications thereof are pos sible. My invention, therefore, is not to be restricted, except insofar as is necessitated by the prior art.

I claim as my invention:

1. A cathode structure comprising a mass 01' sintered tungsten particles having pores therein, portions of the surface of said pores being coated with an oxide 01' said metal and an electron emitting substance on said oxide and a pocket in said mass having a reservoir of said electron emitting substance.

2. A cathode structure comprising a porous mass of sintered tungsten having a pocket therein, an electron-emitting vaporizable substance in said pocket, and means for vaporizing said substance.

WERNER ESPE. 

